4 



side of a leaf, it first increases in size by absorbing the water and after a couple of hours produces one 

 or more tubes which enter the minute pores on the under side of the leaf known as stomata ; then 

 attacking the internal tissue of the leaf they destroy it, and the destruction of the dark green cells of 

 the upper surface of the leaf produces the well-known yellow spot. This operation takes three or four 

 weeks. The fungus then prepares to produce fresh spores. Some of the threads or tubes in the interior 

 of the leaf forming bundles project through the above-mentioned pores upon the under side of the leaf 

 and each produces on its end a small globular body, which develops into a spore, behind this is produced 

 another and another, till they hang down in chains, and this is continued till the fungus is exhausted. 



Sometimes the spores instead of being drifted away by the wind to other leaves, fall upon the same 

 leaf, and attack it again; this produces the secondary spots, but, as a rule, the leaf is exhausted by the 

 time that the spores are produced, and after turing brown drops off. 



As loDg as there are but few spots on the leaf, and the attack is but slight, little harm is done. 

 It is not only the destruction of so much leaf tissue by the fungus which injures the plant, but it 

 appears probable also that the tubes of the fungus suck out the nourishment from the leaf, and as soon 

 as the leaf has no longer a sufficient supply for itself, it perishes. 



Conditions for the germinating of the Spores. 

 Dr. Burck in his examination of the germination of the spores, noticed that spores taken from the 

 same sick spot and deposited in a drop of water, at different periods of the day, did not always germi- 

 nate. By following up this clue he found that, besides air and water, darkness also was a requisite of 

 successful germination. If spores are put in a drop of oxygenated water and exposed to light they do 

 not germinate. Pure sunlight is not essential to prevent their growth. The diffused light of the 

 laboratory at some distance from the window prevented any development. If, however, the spores are 

 taken into the dark, in 2 hours or 2\ hours they germinate and emit the tube. Total darkness, how- 

 ever, is not necessary for this. Further investigation showed that the light absolutely killed the 

 spores, after a short exposure to it, eveu if removed into the dark, they no longer are able to produce 

 the tube. Of spores placed at a distance of six or seven feet from the window for \\ hours most were 

 dead, and after an exposure of an hour and three-quai ters all were dead. This, however, it must be 

 remarked, applies to spores in water only. If kept quite dry they will withstand the sunlight for a 

 long time Coffee leaves with the spores still suspended from the sick spots may be exposed to the 

 influence of sunlight till they are quite dried up without losing life. It is, therefore, the spore swelling 

 with the water which it has absorbed that is killed by the light. Further, it was noticed that the blue 

 rays of the spectrum were the fatal ones. In the red rays the spores grew as rapidly as in complete 

 darkness. Even the strongest petroleum light had no effect upon the spore, the actinic rays being too 

 ■weak to kill it. 



The requisites for germination are thus, water, air and more or less complete darkness. For the 

 further stages it is requisite that it fall upon the under side of a coffee leaf, for on the upper side are 

 none of the stomata by which alone it can penetrate to the inner tissue of the leaf. These observations 

 are not without practical interest, for the injurious effect of sunlight upon the spores explains to us 

 the fact well known to planters that the leaves of the upper branches of untopped trees are seldom 

 attacked so badly as to affect the ripening of the fruit. Repeatedly, Dr. Burck affirms, he learnt from 

 the planters in Java that generally it was the crop of the upper branches that was obtained and that 

 of the lower branches and middle ones that there was reason to fear for. 



Everyone who has seen a plantation in an advanced state of destruction will remember the bare 

 trunk and dead side branches crowned at the top with a few tufts of leaves which have escaped the 

 general destruction. 



It is, therefore, better on the whole not to top the trees, and in the plantations where the trees 

 have already been topped for some years, it is better to let them shoot up again. The lower sides of 

 the upper leaves receive light of higher intensity than the middle and lower branches, and this increase 

 of light is sufficient to kill the spores if damp. Of course, even those leaves of which the under side is 

 fully exposed to sunlight are not free from the possibility of infection by night, but by this exposure 

 their chances of infection are much lessened. 



It might be imagined from this that the destruction of the shade trees would be desirable, but 

 this would not avail much against the disease, as it is on the under side of the leaf that the spore can 

 make its attack and that is shaded by the leaf itself and by the other leaves on the bush. 



Fallen Leaves. 



Most of those who have written about the disease have cautioned planters against allowing the 

 fallen leaves to remain on the ground, fearing that they may affect the healthy leaves. Dr. Burck 

 found, however, that spores taken from fallen leaves did not germinate, the reason being that they were 

 killed by exposure to light as soon as they were wetted by rain or dew. It is indeed quite safe to leave 

 the dead leaves upon the ground whether the upper or lower side be exposed to light. For if a leaf 

 lies upon its upper surface the spores are killed by exposure to light ; if on the lower surface they 

 begin to grow and are then killed by the excessive wet of the rain on the ground. Should the weather 

 be very hot and dry it will be advisable to destroy the leaves. The disease, however, rarely occurs 

 during the dry season Dr. Burck has, he states, only seen such a case three times and then in a 

 plantation of one or two years' growth. 



Infection of the Leaves. 



The spores will not germinate in air however damp it be. They require fluid water ; so that the 

 leaf can only be affected when it is covered with drops of dew or rain. 



Professor Marshall Ward thought that fresh spores put into a drop of water only began to germi- 

 nate after from 12 to 24 hours, and did not enter the leaf for 48 hours after they were put into the 



